The present invention relates to a method of manufacturing a core collimating assembly for applications in DWDM devices.
Dense-Wavelength-Division-Multiplexing (DWDM) systems take advantage of advanced optical technology (e.g., tunable lasers, narrow-band (NB) optical filter, etc.) to generate many wavelength in the range around 1550 nm, which has gained itself the mainstream trend of the optical telecommunication industry nowadays and in the future. Many crucial optical components applied in DWDM systems, such as OADM, multiplexing/demultiplexing modules, optical switches, couplers, optical transceivers, etc., require collimated light beams. Therefore, collimating assemblies thus attain important and wide applications in manufactures of these optical components.
Collimating assemblies may generally be divided into three types as discussed in the following contents.
The first type is Prism type which purely employs a prism or an array of prisms to transfer dispersive light beams into collimated parallel light beams. A related example may be referred to U.S. Pat. No. 4,350,410.
The second type is Lens type which may use spherical lenses, planoconvex lenses, biconvex lenses, single aspherical surface lenses or Gradient Index (GRIN) Lens to achieve the same function as discussed above. Details related please refer to U.S. Pat. Nos. 4,575,194; 4,758,071 and 5446,815.
The third is a combination of the first and second types, which combines both prisms and lenses to form a collimating assembly for gaining collimated parallel light beams. Closely related inventions have been disclosed in U.S. Pat. Nos. 4,609,258 and 5,321,717.
However, in addition to traditional prisms or lenses, filters are also applied to fabricate collimating assemblies, esp. when the corresponding collimating assemblies are provided for thin film filter based DWDM devices. Such collimating assemblies may be acted as 3 or more ports device core. A core collimating assembly for 3-port DWDM devices is the key part for thin film filter based DWDM devices and usually comprises a dual fiber (DF) collimator and a narrow band (NB) filter.
Referring to FIGS. 8 and 9, one embodiment of an improved method of fabricating a lens-type collimating assembly is disclosed in U.S. Pat. No. 5,150,230. Firstly, a flanged split sleeve 48 is formed with axially extending slits 52 and a flange 50 defined with a plurality of radially extending slits 53 arranged in circumferentially spaced relationship from one another. A rod lens 6 is press-fitted into the flanged split sleeve 48. Then, a sleeve portion of a lens assembly 46 is inserted into a stepped sleeve 12, and the flange 50 of the lens assembly 46 is laser-welded to one end surface of the stepped sleeve 12 at four points P in the slits 52 and in some of the slits 53 of the flange 50 on only one side of each slit. In this manner, each point P of the laser welding is set on the only one side of each slit of the flange 50. Therefore, stresses due to shrinkage of the welded portions upon annealing can be made almost zero. This method is tried to eliminate tensile forces produced during the process of annealing the lens-type collimating assembly, but it surely causes more difficulties in the performance of welding and needs more personal skill and extra-care.
Another conventional method of manufacturing such a core collimating assembly is discussed here. Firstly, one or more fiber is inserted into a capillary and fixed with glue or epoxy. Secondly, the end face of the subassembly of the capillary and the fibers is polished to form an angle, preferably 6-8 degrees, which ensures the subassembly has the best light incident angle. Thirdly, the capillary is attached with a GRIN lens by applying epoxy onto the end face of the capillary. Finally, the collimating assembly of the capillary and the GRIN lens is baked for curing the epoxy, in which the temperature should be carefully controlled since a too high temperature will cause the capillary or GRIN lens broken.
Nevertheless, to apply the epoxy around the capillary uniformly and not to stain the fiber is one strict requirement, which demands good personal skills and extra-care on applying the epoxy, to the third process. If the epoxy is not uniformly attached to the capillary, then the GRIN lens may not be attached properly.
A main object of the present invention is to solve the problems as discussed above, that is, to provide a method of manufacturing a collimating assembly which has the advantage of simple performance without the need of special personal skill and extra-care, and which provides a good yields and good thermal stability of the product.
In accordance with one aspect of the present invention, a method of manufacturing a collimating assembly includes the following steps: preparing a GRIN lens subassembly; preparing a dual-fiber (DF) pigtail subassembly; fitting the GRIN lens subassembly and the DF pigtail subassembly together; applying epoxy onto a junction zone between the GRIN lens subassembly and the DF pigtail subassembly; and baking the junction zone for curing the epoxy thereof until the epoxy spreading uniformly over the junction zone due to the so-called capillarity phenomenon.
The GRIN lens subassembly includes a GRIN lens, a filter adhered to an end of the GRIN lens, and a sleeve adhesively fixed around the opposite end of the GRIN lens. The DF pigtail subassembly has a pair of fibers each with one end fixed within a ferrule and a bushing secured around the ferrule. The sleeve and the bushing each have a corresponding mating end thereby forming a junction zone therebetween for facilitating uniformly flowing epoxy thereon in the step of baking the collimating assembly.
The first step of preparing the GRIN lens subassembly also comprises conglutinating a GRIN lens and a filter together, fixing a sleeve around the GRIN lens by applying epoxy therebetween, and properly heating for curing the epoxy.